There have been notable advances in the design and development of artificial robotic hands over the last several decades. The Utah/M.I.T. hand was developed over twenty years ago with three fingers and a thumb. More recently, the Gifu hand and the Shadow Hand have been developed with high levels of dexterity. Because the dexterity of these artificial hands is approaching that of human hands, tactile sensing is very important for the development of intelligent grasp control algorithms. Tactile sensing is also very important in upper limb prosthetics, where a number of mechanical advances have also been recently made. For example, the i-Limb has four fingers and a thumb with one motor for each digit. The Smarthand and Michelangelo hand also have five fingers.
One general problem for upper limb amputees is that they lack proprioceptive feedback about the grip force applied by their prostheses. For this reason, amputees are more likely to drop grasped objects because they do not know exactly how tightly the object is grasped. This is corroborated by recent surveys from amputees which indicate their desire for a level of automatic grasped object slip prevention. However, the detection and prevention of grasped objects from slipping is a difficult problem in general that is important not only for prosthetic hands but also for autonomous robots.
There are several approaches to enhance the flexibility of tactile sensors. The flexibility of silicon-diaphragm sensors can be increased through the incorporation of polymers during the fabrication process. Mounting the sensors on a flexible substrate or using polyimide layers as a connecting material between silicon-diaphragm sensors can also increase the flexibility of the sensors. Another approach is the use of compressible and flexible conductive sheets as a sensing material to increase the size and flexibility of tactile sensors. In this method, flexible sheets are sandwiched by conductive strips. Although these sensors provide good flexibility in a large area, their response, spatial resolution, and sensor size on a large area are limited. Control of dimensions of sensors and sensor elements during the fabrication process is another limitation.
Thus, more sophisticated and more flexible tactile sensing is essential for improved control of tele-operated robotics such as upper limb prostheses and laparoscopic and robot assisted surgery.